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There are different types of COVID-19 tests.

  • Viral tests (NAAT and antigen) are swab or saliva tests that look for current infection. Most self-tests are antigen tests.
  • Antibody tests are blood tests that look for past infection.

Only viral tests are recommended to see if you are currently infected with COVID-19.

Viral tests are swab or saliva tests.

  • They can show if you have a current infection.
  • There are two main types of viral tests: antigen tests and nucleic acid amplification tests (NAATs). Most self-tests are antigen tests.
    • Antigen tests are rapid tests that give results in 10-30 minutes.
      • Antigen tests are less accurate than NAATs. This means that they are more likely to give false results, especially false negatives. Since antigen tests are less accurate, it is recommended that negative tests be repeated at least 48 hours later. See FDA instructions on repeat testing.
      • If you are doing a self-test, it is very important to follow the manufacturer’s step-by-step instructions exactly, including any instructions for repeat testing.
      • Sometimes a follow-up NAAT may be recommended to confirm an antigen test result.
      • Antigen tests are the best test for people who have tested positive in the last 90 days.

    • NAATs, such as PCR and LAMP tests, are usually performed in a laboratory.
      • PCR tests are the most accurate type of NAAT test for COVID-19. NAAT tests are less likely to give false results than antigen tests. They are sometimes used to confirm the results of rapid tests.
      • NAATs detect genetic material from the COVID-19 virus. If you get a COVID infection, this genetic material can stay in your body for up to 90 days. For this reason, NAATs are not recommended for people who have had COVID until 90 days have passed since their first positive test.

  • See Self-tests-free kits and how to test to learn more, including how to tell if your test is good to use after it is past its expiration date.
  • See Understanding Your Viral Test Result and What to do Next for more information.

Antibody tests (also known as serology tests) are blood tests.

  • They might tell you if you had an infection in the past, but they cannot tell you when.
  • They should not be used to test for a current infection or to tell if you are protected from getting COVID-19 in the future.

(swab or saliva tests)
Looks for current infection


(blood tests)
Looks for past infection

(molecular tests e.g., PCR and LAMP*)

(most self-tests are antigen tests)

(serologic test or serology)

How the test works

Detects genetic material (RNA) within the COVID-19 virus

Detects proteins (or antigens) on the surface of the COVID-19 virus

Detects antibodies made by the immune system

How the test is done

Saliva, or swab from nose or throat

Swab from nose or throat

Blood from arm or finger stick

How long it takes to get results

Same day and up to 3 days. Some are rapid (around 20 minutes)

Most are rapid, around 10-30 minutes

Same day and up to 3 days

Over the counter self-tests

A few companies make them

Many companies make them

Not available

*Includes PCR (e.g., Reverse-Transcriptase Polymerase Chain Reaction - RT-PCR) and Loop-Mediated Isothermal Amplification (LAMP)

When to Get a Test

  • If you have COVID-19 symptoms.
  • If you have been a "close contact" to someone with COVID-19. See ph.lacounty.gov/covidcontacts.
  • If you have COVID-19. Testing negative is strongly recommended before ending isolation between Day 6-10. Another reason to test is if you want to stop wearing a mask between Day 6 and Day 10. It is best to use an antigen test for this. See ph.lacounty.gov/covidisolation.
  • Before and after travel. See CDC Travel for current recommendations.
  • Before and/or after attending a gathering or event, especially if you will be around people who are at high risk for severe illness.
  • If recommended by a healthcare professional or Public Health.

Note: There may be other settings that have their own testing requirements.

If you had COVID-19 within the last 90 days, you should test if you have symptoms of COVID-19. You should also test if you are a close contact to someone with COVID-19 and it has been 31-90 days since your first positive test. Otherwise, testing is not usually recommended. If you do test within 90 days of your first positive COVID-19 test, use an antigen test rather than a NAAT.

Understanding Your Viral Test Results and What to do Next

Talk with your doctor to make sure you understand what your test result means and any next steps. If you took a self-test, read the manufacturer’s instructions on how to interpret the test results. If you need advice about what to do next, you can also call the DPH COVID-19 information line at 1-833-540-0473.

Your COVID-19 Test was POSITIVE (POS)

The test detected the COVID-19 virus. It is very likely you have COVID-19 and could spread it to others.

You need to isolate. Stay home and away from others for at least 5 days, even if you do not have symptoms. Follow all instructions at ph.lacounty.gov/covidisolation.

Important: If you have symptoms, ask about COVID-19 treatment right away, even if your symptoms are mild. Treatment can prevent you from getting very sick. Many adults and some children qualify for free medicines, such as Paxlovid. The oral medicines must be started within 5 days from the start of your symptoms, so don’t delay. Talk to your doctor or call the Public Health Tele-Health Service 1-833-540-0473 – open 7 days a week, 8:00 am – 8:30 pm. For more information, visit ph.lacounty.gov/covidmedicines.

Your COVID-19 Test was NEGATIVE (NEG)

A negative COVID-19 result means the test did NOT detect the COVID-19 virus at the time you took the test.

If you have symptoms of COVID-19

It is possible that the test is wrong and that you are infected. This can happen for many different reasons including if the test was taken too early, if your specimen sample wasn’t collected well, or if the amount of virus was too low to be detected by the test.

If you used a self-test, take steps to make sure it isn’t a false negative. Make sure you read and follow all test instructions correctly. Repeat the test at least once at least a day later. See FDA instructions on repeat testing.

Follow the LAC DPH COVID-19 guidance at Learn about Symptoms and What to do If you are Sick.

If you don’t have symptoms of COVID-19

It is unlikely you have COVID-19.

If your negative test was a self-test, make sure you read and follow all test instructions correctly. Some self-tests are designed to be used in a series (also known as serial testing). Multiple negative tests increase the confidence that you are not infected with the virus that causes COVID-19. This is especially important if you are a close contact. See FDA instructions on repeat testing.


COVID-19 antibody tests (also known as serology tests) are blood tests that are used to look for antibodies to SARS-COV-2 (the virus that causes COVID-19). If we get COVID-19 or a COVID-19 vaccine our body’s immune system responds. It makes antibodies and prepares our immune cells to be ready to fight the virus in the future.

COVID-19 antibody tests do not look for the actual SARS-CoV-2 virus itself. They can be used to help figure out if someone was infected with COVID-19 in the past. It takes about one to three weeks after becoming infected for the body to make enough antibodies to be found by a test. Some people may take even longer, and some people who were infected with COVID-19 may never develop antibodies. NONE of the currently authorized tests are recommended to see if people have been successfully vaccinated against COVID-19.

COVID-19 antibody tests cannot tell a person:

  • When or if they definitely had COVID-19
  • Whether or not they are protected (immune) from COVID-19
  • Whether it is safe to travel or spend time with other people
  • Whether they need to isolate
  • Whether they should or should not get vaccinated
  • Whether or not their vaccine is working.

Antibody tests are not 100% accurate, so false results may occur. Talk to your doctor before being tested for antibodies. Your doctor can help you decide if you should be tested and, if you are tested, tell you what your results mean. To learn more about antibody tests, visit the CDC webpage.


  • CDC COVID-19 Testing: webpage with links to pages on types of tests and FAQs
  • FDA Coronavirus Basics: webpage explains the different types of tests, and how they are performed and approved.

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Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.

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